This invention relates to hydraulically or pneumatically actuated motors, and is more particularly directed to a torsional fluid-dynamic muscle which can be made of small diameter and incorporated into a steering or articulation section of a flexible elongated probe. The invention is also directed to improvements in borescopes and/or endoscopes which permit four-way steering of the distal end of an insertion tube without reliance on the conventional, but delicate and trouble-prone cable-type steering movement. Additionally, the torsional fluid-dynamic muscle or motor of this invention has other applications including rotary actuators and gauges, grabbers, and supports for remote tools. The invention can also be regarded as a pump for converting an angular or torsional force to a fluid pressure.
Borescopes or similar flexible probes are generally configured as an elongated flexible insertion tube with a viewing head at its distal or forward end and a control housing for controlling or steering the distal or forward end. The typical borescope has a bendable tubular steering section or articulation section at the distal end adjacent the viewing head. The steering section comprises a series of alternating wobble washers and spacers, with control cables that extend through the wobble washers and then through the remainder of the flexible insertion tube. The steering cables connect with a steering control unit in the control section. Each such pair of cables is differentially displaced to bend the steering section. The viewing head can be remotely oriented to facilitate inspection of an object. Borescopes are often required to bend in narrow, tortuous passageways, so the diameter of the borescope is often quite limited, e.g. 6 mm. Also, the pathway to the object or target can be quite long, which then requires the insertion tube and the steering cables to be rather long, e.g. fifteen meters or more.
A number of cable-actuated articulation or steering mechanisms are known, and typical ones are discussed in U.S. Pat. Nos. 3,610,231; 3,739,770; 3,583,393; 3,669,098; 3,779,151; and 4,347,837. Another steering mechanism is described in U.S. Pat. No. 4,700,693.
These cable-actuated articulation mechanisms require the cables to have a significant amount of slack or play because bends and coils in the insertion tube effectively shorten the cables and because the articulation section bends at discrete points rather than following a smooth arc. However, in many applications the articulation section must be bent rather precisely to penetrate the tortuous passages into the area to be inspected without damaging delicate engine parts. For these reasons, cable tension must be limited and cable slack must be minimized. However, where the insertion tube is long, extra cable slack is often included to accommodate the increased cable tightening due to the substantial coiling and bending of the insertion tube through which the steering cables pass. A proposed arrangement to permit steering cables to be kept short as possible is described in U.S. Pat. No. 4,794,912. That patent describes a "muscle," i.e. a linear traction motor, that addresses many of the problems found in these prior-art steering mechanisms. Specifically, fluid dynamic muscles mounted adjacent the distal end of the insertion tube are actuated by pneumatic or hydraulic pressure supplied through small flexible tubes within the borescope insertion tube. Short steering cables connect the respective muscles with the articulation mechanism. As fluid pressure is applied differentially to a pair of muscles, the cables move differentially and the articulation mechanism bends the steering section a desired amount.
While this system avoids many of the above-mentioned problems, especially those associated with extremely long cables, there are remaining problems because of the reliance on an otherwise conventional cable steering mechanism. The steering section is rather complex and expensive, and does not follow a natural arc, as mentioned before. Further simplification, by replacing the cable drive steering mechanism, would be required to reduce or eliminate these residual drawbacks.
A hydraulic or pneumatic bending neck is proposed in copending and commonly-assigned U.S. patent application Ser. No. 538,232, filed June 18, 1990. In that arrangement, an articulation or steering mechanism is formed of an elongated fluid-controlled muscle that has a flexible spine arranged in the axial direction along one side and disposed in the interface between the bladder and the braid. The braid confines the bladder such that when the bladder is inflated, the bladder and braid expand laterally, but shorten axially. Because of the spine, the braid can shorten only on the side away from the spine, so the spine defines a bending plane for the bending neck. Preferably, the spine is arcuately biased in one direction so that when no pressure is applied the bending neck is bent in one direction in the bending plane. At full pressure the bending neck is bent in the opposite direction, and at an intermediate pressure, the bending neck is held straight.
This type of arrangement is capable of two-directional steering, i.e., bending that is confined to a single bending plane. It would be desirable to have four-way steering with fluid-dynamic bending, but as aforesaid, the bending neck is difficult to adapt for deflection in orthogonal directions.